The present invention relates to a hull protection system for a liquefied gas ship.
Generally, a liquefied gas ship has a structure as shown in FIG. 1 in which a tank body 1 made of aluminum alloy is covered on its outer surface with a relatively hard insulation material 6 such as polyurethane foam and is supported by a plurality of heat insulating tank supports 2 which in turn are arranged on a bottom of an inner shell 3 of a hull. Since the tank body 1 may be expanded or contracted due to temperature change caused by absence or presence of liquefied gas in it, to attach or bond the insulation material 6 at its edge to the tank support 2 would cause the material 6 to be distorted, resulting in damage of the material 6. Therefore, the material 6 directly mounted on the tank body 1 is not attached or bonded at its edge to the tank support 2; but, as shown in FIG. 2, a heat insulating material 16 such as glass wool is filled between the edge of the material 6 and the tank support 2 for prevention of transmission of external heat to the tank body 1 through a gap between the edge of the material 6 and the tank support 2.
In the event of leakage of liquefied gas stored at extremely low temperature in the tank body 1, the inner shell 3 may be exposed to the leaked liquid and turned to low temperature, becoming brittle. In order to overcome this, there have been proposed that the inner shell 3 is made of the same material as the tank body 1 or that a trough 17 is arranged as shown by imaginary lines in FIG. 2 to receive the liquefied gas leaked to an outer periphery of the tank support 2.
However, to make the inner shell 3 of the same material as the tank body 1 will extremely increase the cost for constructing the liquefied gas ship and therefore is next to impossible for practical application. To provide the trough 17 for each tank support 2 is also disadvantageously uneconomical.
To solve the above problems, the present invention has as its object to provide a hull protection system for a liquefied gas ship which is simple in structure so as to not increase a cost for construction and which is reliable for collection and disposal of leaked liquid to prevent the inner shell from becoming brittle due to low temperature.